1. Technical Field of the Invention
The present invention relates to an apparatus for restricting or preventing the flow of water across the joints of foundation elements, such as between or along individual diaphragm wall panels or between or along individual secant wall piles. The present invention also relates to a method of installing a waterstop at or near the joints between adjacent foundation elements.
2. Prior Art
A diaphragm wall is made by casting a series of concrete panels, which may be reinforced, in excavated trenches as described, for example, in EP 0 101 350 and EP 0 402 247. In some cases, alternate xe2x80x98primaryxe2x80x99 panels are constructed first, followed by infill (i.e. closing) xe2x80x98secondaryxe2x80x99 panels. The installation sequence would be, for example, panels 1, 3, 5, 7, 9, 11 etc. followed by panels 2, 4, 6, 8, 10 etc. In other cases, only a few xe2x80x98primaryxe2x80x99 panels are first constructed, for example panels 1, 10 and 20. Following this, a series of xe2x80x98continuityxe2x80x99 panels 2, 11, 3, 12 etc. are installed, with the diaphragm wall being completed by xe2x80x98closingxe2x80x99 panels 9 and 19. All primary panels require the use of shutters at each edge of their respective trenches in order to provide well-defined edges to each panel so as to ensure that the joins between adjacent panels may be made watertight. Continuity panels, in contrast, require only one shutter at the edge of the trench furthest away from the previously cast panel. No shutters are required for closing panels. The shutters are conventionally known as xe2x80x98stop-endsxe2x80x99, and provide the concrete at each vertical edge of the panels with a predetermined shape.
In order to reduce water leakage across the joints between panels, it is possible to install a waterbar between adjacent panels with particular types of stop end as described in EP0101350. A waterbar comprises a strip of suitable material, for example rubber or PVC, which has one longitudinal edge embedded in the edge of one cast panel and the other longitudinal edge embedded in the adjacent panel. Preferably, the waterbar extends over substantially the entire height of the diaphragm wall. Such a waterbar may be installed by employing a stop-end provided with a slot in its face into which the waterbar may be fitted, with about one half of its width remaining exposed. When concrete is poured into the trench on this side of the stop-end and allowed to set, the stop-end may subsequently be removed so as to leave approximately half the waterbar embedded in the resulting concrete panel. When the next panel is cast, the remaining exposed portion of the waterbar will become embedded in concrete, thereby resulting in a seal between the two adjacent panels. Typical waterbars have beaded longitudinal edges, giving the waterbar a dumb-bell shaped cross-section, with an optional central bulb.
As is well-known, concrete does not bond well to rubber or PVC; therefore, loss of intimate contact can occur between the concrete foundation element and the waterbar. There is therefore a risk that water will leak through the joint. The loss of intimate contact may be a result of the way in which the foundation element and waterbar were installed or it may be due to the relative movement of adjacent elements.
In United Kingdom patent application 2325262, a two-part hydrophilic waterbar was demonstrated. If the hydrophilic element becomes wetted, as a result of water leaking through the joint, the hydrophilic material swells, thereby forming a seal between the two adjacent members.
There are a number of limitations/problems associated with known waterbar systems. For example, all of the known types of waterbars require the use of a stop-end to facilitate the installation of the waterbar. However, in some underground structures it may not always be possible or desirable to use stop-ends between adjacent elements. In these cases a waterbar can not be installed and so if the installation of a waterbar is required, the choice of construction of the diaphragm wall panels is restricted. For example, diaphragm walls can be excavated by means of xe2x80x9chydromillsxe2x80x9d. A hydromill is an apparatus for drilling into the ground and is equipped at the base with one or more pairs of contra-rotating drums. The drums cut the soil which is then excavated from the base by hydraulic means, such as by the circulation of drilling muds. Usually, when constructing diaphragm walls using this apparatus, a series of primary and secondary panels are formed wherein the second panels xe2x80x9ccut backxe2x80x9d into the vertical edge of the primary panels. Stop-ends are not normally used, in which case it is not possible to install a waterbar.
Furthermore, underground structures such as secant pile walls, which comprise a series of primary (conventionally called xe2x80x9cfemalexe2x80x9d) and secondary (conventionally called xe2x80x9cmalexe2x80x9d) piles to not involve the use of stop-ends. Pile construction can be by a variety of methods such as oscillated casing with rotary rig or grab, CFA methods or rotary boring without casing. At present there are no suitable apparatus which can be installed for restricting the flow of water along or across the vertical joints in secant pile walls.
Another limitation suffered by the known waterbar systems, is that although the waterbar will substantially prevent the flow of water horizontally across the joint between adjacent elements, water can still rise up the joint in a vertical direction between the two panels. In order to demonstrate this consider: a peripheral diaphragm wall which is installed in soil strata, where the lower end of the diaphragm wall is situated in water-bearing strata. Assume that a vertical waterbar has been effectively installed across the joints between adjacent panels, at or near the centre of the wall thickness, and that it extends to the base of the diaphragm wall.
After the wall has been exposed (e.g. for a basement) the vertical waterbar will prevent movement of water horizontally, from behind the diaphragm wall through to the exposed face. However, there is a potential for water to rise up the joint between two panels in the zone between the exposed face and the waterbar.
The present invention seeks to mitigate the aforementioned limitations and provides a waterstop, and a method of installing the same, which serves to resist the flow of water along or across the joints between adjacent foundation elements. The waterstop of the present invention does not depend upon the provision of a stop-end for its installation, and can therefore be advantageously employed in subterranean constructions such as secant pile walls and diaphragm walls, including those excavated by means of hydromills. It should however be appreciated that in many cases the elements will still be provided with stop-ends in order to provide the concrete at each vertical edge with a predetermined shape.
The installation of a waterstop according to the present invention is particularly appropriate for xe2x80x9copen borexe2x80x9d operations in which the soil is excavated and the resultant hole is then filled with concrete or grout.
According to one aspect of the present invention, there is provided a waterstop for resisting the flow of water along the interface between two adjacent foundation elements, the waterstop comprising one or more longitudinal strips of hydrophilic material, characterised in that the waterstop forms an integral part of one of the adjacent foundation elements and wherein the hydrophilic strips extend vertically from a position at or near the top of the foundation element to a position at or near the base of the element.
The strip(s) of hydrophilic material are preferably supported by one or a number of support elements. The support element(s) may be advantageously made from a geotextile material which may or may not exhibit hydrophilic properties. However, any other suitable material can be used including a sheet of supporting material.
An important aspect of the waterstop of the present invention is that the waterstop preferably forms an integral part of the foundation element into which it is installed. Unlike known systems, the waterstop does not span across the joint and into both of the adjacent elements. As such, the waterstop does not require the provision of a stop-end to facilitate the installation.
According to a second aspect of the present invention, there is provided a method of installing a waterstop for resisting the flow of water along and/or between adjacent foundation elements, the method comprising the steps of:
i) constructing a series of primary foundation elements at a number of predetermined positions in the ground;
ii) excavating a bore in the ground adjacent to one of the primary foundation elements;
iii) lowering a waterstop comprising one or a number of longitudinal strip(s) of hydrophilic material into the bore, such that the strips extend vertically from a position at or near the top of the bore to a position at or near the base of the bore; and
iv) pumping concrete or grout into the bore so as to form a secondary foundation element, wherein the waterstop forms an integral part of the resulting secondary foundation element.
Advantageously, when the concrete or grout is pumped into the base, the arrangement is such that, as the concrete or grout fills the bore, the strips of hydrophilic material of the waterstop are pushed towards the adjacent panel.
The flow of concrete as it is poured into the bore, naturally serves to push the waterstop towards the primary panel. In addition, a rolling means may advantageously be provided at the lower end of the waterstop, between the hydrophilic strip(s) and the support element. The rolling means preferably comprises a roller or wheel which is connected about it central axis to a lever. The lever is connected to the support element such that, the lever pivots about the support element under the weight of the concrete or by some other means, thereby causing the roller to push against the hydrophilic strip. The strip is then pushed towards the adjacent existing concrete edge.
According to a third aspect of the present invention, there is provided a foundation element having a waterstop formed therein, wherein the waterstop comprises one or more longitudinal strips of hydrophilic material, wherein the hydrophilic strips extend vertically from a position at or near the top of the foundation element to a position at or near the base of the element.
The waterstop of the present invention is conveniently installed in the secondary elements after the formation of the primary elements. For example, in the case of a diaphragm wall, a series of alternate xe2x80x9cprimaryxe2x80x9d panels are constructed, and the region between each pair of primary elements is excavated. One or more waterstops can then be advantageously lowered into either side of the excavated hole near the adjacent primary panels. Concrete is then pumped into the excavated hole to form the so-called xe2x80x9csecondaryxe2x80x9d panel. As the concrete enters the excavated hole and begins to fill it, the strips of material of the waterstop are pushed by the concrete towards the adjacent panel. Alternatively, one or a few xe2x80x9cprimaryxe2x80x9d element(s) may be constructed and the second, third, forth etc elements are formed consecutively in turn. In this case, only the side of the foundation element which is adjacent the pre-formed concrete element will be provided with a waterstop.
The same techniques can advantageously be applied to all open bore constructions, such as secant piled walls, wherein a series of primary elements are installed followed by a number of secondary elements which are advantageously provided with a waterstop of the present invention.
In order to prevent the flow of water in a vertical fashion between adjacent foundation elements, there may advantageously be provided one or a pair of supplementary elements which extend orthogonally from the longitudinal axis of the waterstop element. These elements are preferably positioned at a predetermined level either side of the waterstop element and serve to resist and/or absorb water that rises in a vertical fashion up the waterstop. The supplementary elements are preferably chevron or wedge shape and are affixed to the waterstop such that one edge runs parallel to the edge of the waterstop and the other side extends from an apex near the lower end of the waterstop. This shape is particularly beneficial since as concrete enters the bore from the bottom and rises up the sides of the waterstop, the supplementary elements are encouraged towards the hydrophilic strips of material. Furthermore, any water that rises from below will come into contact with the supplementary elements and be blocked and/or absorbed. The supplementary elements are preferably provided with one or more strips of hydrophilic material.